1. Field of the invention:
This invention relates generally to devices of the class which arc responsive to motion and/or orientation change relative to the gravitational field. The invention relates more particularly to a novel pendulum-type motion and orientation responsive device useful as a seismic, intrusion, or tilt alarm or the like and to a novel automatic normalizing circuit for the device and other purposes.
2. Prior Art:
Simply sated, motion and/or orientation responsive devices of the class to which this invention pertains comprise a pendulum pivotally mounted on a support to be disposed in motion and/or orientation responsive relation to an object or other means to be monitored in such a way that a disturbance in the form of motion, or more accurately a change in motion state, i.e. acceleration, and/or a change in the orientation of the object relative to the gravitational field cause(s) relative angular movement of the pendulum and support with respect to one another, and means for detecting such relative angular movement. This relative angular movement of the pendulum and its support may occur in any one of the following modes: (a) rotation of the pendulum on its pivot axis relative to both the pendulum support and the gravitational field while the support remains in a fixed orientation about the pendulum pivot axis relative to the gravitational field; (b) a change in the orientation of the pendulum support about the pendulum pivot axis relative to the gravitational field while the pendulum remains in its normal vertical orientation relative to the gravitational field; (c) simultaneous rotation of the pendulum on its pivot axis relative to the gravitational field and a change in the orientation of the pendulum support about the pendulum pivot axis relative to the gravitational field.
It is important to note at the outset that, as indicated above, the expression "orientation relative to the gravitational field" and other similar expressions used herein refer to orientation relative to the gravitational field about the pendulum pivot axis.
Devices of this kind are responsive to both motions, or more accurately accelerations (i.e. changes in motion state) of the pendulum support laterally of the pendulum and a change in the orientation of the pendulum support relative to the gravitational field. These motion and orientation changes produce one of the above modes (a), (b), (c) of relative angular movement of the pendulum and its support. Such relative angular movement is detected by the detection means of the device and may activate an alarm or trigger some other action.
The prior art is replete with an assortment of pendulum-type motion and/or orientation responsive devices of the class described. Following is a list of prior patents disclosing such devices:
U.S. Pat. No. 1,870,347 (Roberts): Discloses a mass movement detector having a pendulum supported at its upper end and actuated by mass movement of earth to engage the lower end of the pendulum with a surrounding electrical contact for energizing an electrical alarm circuit.
U.S. Pat. No. 2,448,181 (Holm): Discloses an intrusion/fire alarm having a pendulum supported at its upper end for generating an alarm in response to a fire or intrusion.
U.S. Pat. No. 3,991,178 (Hamilton): Discloses a boat intrusion alarm having a pendulum supported at its upper end and actuated by tilting of the boat in response to an intrusion thereon to actuate an alarm.
U.S. Pat. No. 4,214,238 (Adams et al): Discloses a seismic trigger having an inverted compound pendulum pivoted at its center with its mass distributed rather than concentrated and the greater extension of its mass above its pivot and whose rotation in response to a seismic disturbance actuates a photoelectric sensor.
U.S. Pat. No. 4,262,289 (Rivera): Discloses a seismic alarm having hanging metal straps mounting confronting electrical contacts and a weight attached to one strap to form a pendulum which swings in response to a seismic disturbance to close the contacts.
U.S. Pat. No. 4,297,690 (Baker): Discloses earthquake alarms with both top and bottom supported pendulums whose weighted ends are engagable with surrounding electrical contacts to energize electrical alarms in response to seismic disturbances.
U.S. Pat. No. 4,679,033 (Hwang): Discloses a vibration sensor having a flexible, bottom supported pendulum with an upper conical weight engagable with a central electrical contact to energize an electrical alarm in response to vibrations.
U.S. Pat. No. 4,381,504 (Bitko): Discloses a vibration and tilt alarm with a hanging pendulum whose lower weight is engagable with a surrounding electrical contact to energize an electrical alarm circuit.
U.S. Pat. No. 4,484,186 (Wood): Discloses an earthquake alarm having a top supported pendulum engagable with a surrounding ring electrical contact to energize an alarm circuit in response to a seismic disturbance.
U.S. Pat. No. 4,575,713 (Piper): Discloses an intrusion alarm to be hung on a door knob and having a bottom supported flexible pendulum engagable with a surrounding electrical contact to energize an alarm in response to opening of the door.
U.S. Pat. No. 4,364,033 (Tsay): Discloses a seismometer responsive to both horizontal and vertical seismic motions.
From the above discussion of the listed patents, it will be understood that their devices are essentially pendulum-type motion and/or orientation responsive devices. These and other similar devices have certain deficiencies which the present invention overcomes. Among the foremost of these are relatively low sensitivity, complexity, large size and/or weight, necessity of being supported in a precise orientation relative to the gravitational field, necessity of being initially "zeroed" by manual adjustment, and unpleasing appearance.